学习apache commons-io 1.4类库中的FileCleaner(文件清除器） 它被用来清理象上传大文件时产生的临时文件之类，这些临时文件在不再被使用的时候会自动被删除.这会被org.apache.commons.io.FileCleaningTracker的一个实例启动的一个守护线程默默执行.共有三个类： 1、 类FileDeleteStrategy
import java.io.File;import java.io.IOException;public class FileDeleteStrategy { public static final FileDeleteStrategy NORMAL = new FileDeleteStrategy("Normal"); public static final FileDeleteStrategy FORCE = new ForceFileDeleteStrategy(); private final String name; protected FileDeleteStrategy(String name) { this.name = name; } public boolean deleteQuietly(File fileToDelete) { if (fileToDelete == null || fileToDelete.exists() == false) { System.out.println("File delled!!"); return true; } try { return doDelete(fileToDelete); } catch (IOException ex) { return false; } } public void delete(File fileToDelete) throws IOException { if (fileToDelete.exists() && doDelete(fileToDelete) == false) { throw new IOException("Deletion failed: " + fileToDelete); } } protected boolean doDelete(File fileToDelete) throws IOException { return fileToDelete.delete(); } public String toString() { return "FileDeleteStrategy[" + name + "]"; } static class ForceFileDeleteStrategy extends FileDeleteStrategy { ForceFileDeleteStrategy() { super("Force"); } protected boolean doDelete(File fileToDelete) throws IOException { // FileUtils.forceDelete(fileToDelete); return true; } }}2、FileCleaningTracker类，这个类用于跟踪要删除的文件import java.io.File;import java.lang.ref.PhantomReference;import java.lang.ref.ReferenceQueue;import java.util.Collection;import java.util.Vector;public class FileCleaningTracker { ReferenceQueue q = new ReferenceQueue();//引用队列 final Collection trackers = new Vector(); // synchronized /** * Whether to terminate the thread when the tracking is complete. */ volatile boolean exitWhenFinished = false; //用于删除文件的线程 Thread reaper; public void track(File file, Object marker) { track(file, marker, (FileDeleteStrategy) null); } public void track(File file, Object marker, FileDeleteStrategy deleteStrategy) { if (file == null) { throw new NullPointerException("The file must not be null"); } addTracker(file.getPath(), marker, deleteStrategy); } public void track(String path, Object marker) { track(path, marker, (FileDeleteStrategy) null); } public void track(String path, Object marker, FileDeleteStrategy deleteStrategy) { if (path == null) { throw new NullPointerException("The path must not be null"); } addTracker(path, marker, deleteStrategy); } private synchronized void addTracker(String path, Object marker, FileDeleteStrategy deleteStrategy) { // synchronized block protects reaper if (exitWhenFinished) { throw new IllegalStateException("No new trackers can be added once exitWhenFinished() is called"); } if (reaper == null) { reaper = new Reaper(); reaper.start(); } trackers.add(new Tracker(path, deleteStrategy, marker, q)); } public int getTrackCount() { return trackers.size(); } public synchronized void exitWhenFinished() { // synchronized block protects reaper exitWhenFinished = true; if (reaper != null) { synchronized (reaper) { reaper.interrupt(); } } } private final class Reaper extends Thread { Reaper() { super("File Reaper"); setPriority(Thread.MAX_PRIORITY); setDaemon(true);//设置为守护线程 } public void run() { // thread exits when exitWhenFinished is true and there are no more tracked objects while (exitWhenFinished == false || trackers.size() > 0) { Tracker tracker = null; try { // Wait for a tracker to remove. tracker = (Tracker) q.remove(); } catch (Exception e) { continue; } if (tracker != null) { tracker.delete(); tracker.clear(); trackers.remove(tracker); } } } } private static final class Tracker extends PhantomReference {//虚引用 private final String path; private final FileDeleteStrategy deleteStrategy; Tracker(String path, FileDeleteStrategy deleteStrategy, Object marker, ReferenceQueue queue) { super(marker, queue); this.path = path; this.deleteStrategy = (deleteStrategy == null ? FileDeleteStrategy.NORMAL : deleteStrategy); } public boolean delete() { return deleteStrategy.deleteQuietly(new File(path)); } }}3、FileCleaner类import java.io.File;public class FileCleaner { /** * The instance to use for the deprecated, static methods. */ static final FileCleaningTracker theInstance = new FileCleaningTracker(); public static void track(File file, Object marker) { theInstance.track(file, marker); } public static void track(File file, Object marker, FileDeleteStrategy deleteStrategy) { theInstance.track(file, marker, deleteStrategy); } public static void track(String path, Object marker) { theInstance.track(path, marker); } public static void track(String path, Object marker, FileDeleteStrategy deleteStrategy) { theInstance.track(path, marker, deleteStrategy); } public static int getTrackCount() { return theInstance.getTrackCount(); } public static synchronized void exitWhenFinished() { theInstance.exitWhenFinished(); } public static FileCleaningTracker getInstance() { return theInstance; } //简单测试 public static void main(String[] args){ getInstance().track("c:\\java\\1.txt", new Object()); getInstance().track("c:\\java\\2.txt",new Object()); System.gc(); System.exit(0); } }
